The overall goal of this project remains to understand how the properties of arthropod-borne viruses enable them to replicate in widely different hosts and to cause in their vertebrate hosts a variety of different disease states. Our experimental systems will involve the study of Sindbis and dengue viruses (genera alpha- and flavivirus: Family Togaviridae) as well as vesicular stomatitis virus (Family Rhabdoviridae) in vertebrate and mosquito cells. It is expected that what we learn of these viruses at the cellular level will eventually enhance our understanding of what occurs in the whole organism, vertebrate or invertebrate. Working with VSV in A. albopictus cells, we shall study how the rate of viral RNA synthesis is related to inhibiton of protein synthesis and eventually to cell killing. The biochemical lesion which leads to inhibition of protein synthesis will be investigated. Arthropod-borne viruses, because of their wide host range, are eminently suited for the generation and study of host-range mutants. We shall seek additional host-range mutants and attempt to determine in molecular terms why these mutants are restricted in their ability to replicate in a given cell type. We shall also determine nucleotide sequence changes which are specifically associated with the host-range phenotype. The replication of Sindbis virus in A. albopictus cells is efficiently inhibited by the nucleoside analog, ribavirin. On the other hand, this compound under certain conditions has little or no effect on viral replication in BHK cells. We shall continue to identify those properties of different host cells which determine the efficacy of ribavirin and we shall assess its anti-viral action in different organs of the whole animal. Much less is known of the strategy of replication of dengue virus and flaviviruses in general than is known about either alphaviruses or rhabdoviruses. In this project we intend to study the patterns of protein processing and the functions of the different virus-specified proteins in infected cells. In particular the processing of specific proteins will be related to viral morphogenesis and maturation.